Dielectric structure

ABSTRACT

Dielectric structures particularly suitable for use in capacitors and having a textured surface are provided, together with methods of forming these structures. Such dielectric structures show increased adhesion of subsequently applied conductive layers.

BACKGROUND OF THE INVENTION

[0001] The present invention relates generally to the field ofdielectric structures. In particular, the present invention relates tothe field of dielectric structures suitable for use in capacitormanufacture.

[0002] Laminated printed circuit boards, as well as multichip modules,serve as support substrates for electronic components, such asintegrated circuits, capacitors, resistors, inductors, and othercomponents. Conventionally, discrete passive components, e.g. resistors,capacitors and inductors, are surface mounted to the printed circuitboards. Such discrete passive components can occupy up to 60% or greaterof the real estate of a printed circuit board, thus limiting the spaceavailable for the mounting of active components, such as integratedcircuits. The removal of passive components from the printed circuitboard surface allows for increased density of active components, furtherminiaturization of the printed circuit board, increased computing power,reduced system noise and reduced noise sensitivity due to shortenedleads.

[0003] Such removal of discrete passive components from the printedcircuit board surface can be achieved by embedding the passivecomponents within the laminated printed circuit board structure.Embedded capacitance has been discussed in the context of capacitiveplanes providing non-individual or “shared” capacitance. Capacitiveplanes consist of two laminated metal sheets insulated by a polymerbased dielectric layer. Shared capacitance requires the timed use of thecapacitance by other components. Such shared capacitance fails toadequately address the need for embedded capacitors that still functionas discrete components.

[0004] U.S. Pat. No. 6,068,782 (Brandt et al.) discloses a method ofproviding individual embedded capacitors including the steps ofpatterning a photoimageable low dielectric constant material on top of abottom electrode material, depositing capacitance dielectric material byeither filling or partially filling the pattern, and then fabricating acapacitor top electrode. Such capacitor dielectric material typicallyhas a high dielectric constant, such as a ceramic or metal oxide. Oneproblem with using such ceramics or metal oxides is that they may bedifficult to metallize, i.e. to fabricate an electrode on, usingtechniques conventionally used in the printed circuit board industry.

[0005] U.S. Pat. No. 6,180,252 B1 (Farrell et al.) discloses high energystorage devices for use in semiconductors. This patent disclosesconformally coating a dielectric material on a silicon substrate wherethe silicon substrate is three-dimensional. In this way, the surface ofthe dielectric material remains smooth and not textured.

[0006] There is a need for capacitors, particularly embeddablecapacitors, having high dielectric constant capacitance dielectricmaterial that are easier to fabricate electrodes on than conventionalhigh dielectric constant capacitance dielectric material.

SUMMARY OF THE INVENTION

[0007] It has been surprisingly found that the adhesion of platedelectrode layers to high dielectric constant material can be improved byproviding increased surface roughness of the dielectric material. Suchincreased surface roughness is preferably provided through the use ofremovable porogens.

[0008] The present invention provides a capacitor structure including afirst conductive layer, a second conductive layer and a multilayerdielectric structure disposed between the first and second conductivelayers, wherein the multilayer dielectric structure includes a firstdielectric layer and a second dielectric layer, wherein the firstdielectric layer has a textured surface. Preferably, the texturedsurface of the first dielectric layer is in intimate contact with thefirst conductive layer.

[0009] The present invention also provides a method of improving theadhesion of a plated conductive layer to a dielectric structureincluding the steps of depositing on a dielectric layer a top dielectriclayer comprising porogen, removing the porogen to provide a texturedsurface on the top dielectric layer, and depositing a conductive layeron the textured surface of the top dielectric layer.

[0010] Additionally, the present invention provides a printed circuitboard including an embedded capacitance material, wherein the embeddedcapacitance material includes the multilayer dielectric structuredescribed above.

[0011] Further, the present invention provides a method of manufacturinga multilayer laminated printed circuit board including the step ofembedding a capacitance material in one or more layers of the multilayerlaminated printed circuit board, wherein the embedded capacitancematerial includes the multilayer dielectric structure described above.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 illustrates a dielectric structure of the present inventionhaving a first dielectric layer having a textured surface, not to scale.

[0013]FIG. 2 illustrates a capacitor of the present invention having afirst dielectric layer having a textured surface, not to scale.

DETAILED DESCRIPTION OF THE INVENTION

[0014] As used throughout this specification, the followingabbreviations shall have the following meanings, unless the contextclearly indicates otherwise: ° C.=degrees Centigrade; rpm=revolutionsper minute; mol=moles; hr=hours; min=minute; sec=second; nm=nanometers;cm=centimeters; in.=inches; and wt %=percent by weight.

[0015] The terms “printed wiring board” and “printed circuit board” areused interchangeably throughout this specification. “Depositing” and“plating” are used interchangeably throughout this specification andinclude both electroless plating and electrolytic plating. The term“(meth)acrylic” includes both acrylic and methacrylic and the term“(meth)acrylate” includes both acrylate and methacrylate. Likewise, theterm “(meth)acrylamide” refers to both acrylamide and methacrylamide.“Alkyl” includes straight chain, branched and cyclic alkyl groups. Theterm “porogen” refers to a pore forming material, that is a polymericmaterial dispersed in a dielectric material that is subsequently removedto yield pores, voids or free-volume in the dielectric material. Thus,the term “removable porogen” will be used interchangeably with“removable polymer” or “removable particle” throughout thisspecification. The terms “pore” and “void” are used interchangeablythroughout this specification. “Cross-linker” and “cross-linking agent”are used interchangeably throughout this specification. “Multilayer”refers to two or more layers. The term “dielectric structure” refers toa layer or layers of dielectric material.

[0016] All percentages are by weight, unless otherwise noted. Allnumerical ranges are inclusive and combinable in any order, except whereit is clear that such numerical ranges are constrained to add up to100%.

[0017] The present invention provides a capacitor structure including afirst conductive layer, a second conductive layer and a multilayerdielectric structure disposed between the first and second conductivelayers, wherein the multilayer dielectric structure has a top and bottomsurface, wherein at least one of the top and bottom surfaces istextured. Preferably, such textured surface is in intimate contact withat least one of the first and second conductive layers. “Textured”refers to a surface having sufficient irregularities or topography toprovide increased adhesion of subsequently applied electrode orconductive layers. Suitable topographies include, but are not limitedto, channels, ridges, pores or voids, depressions, grooves, nooks, andcrannies. A textured surface may include more than one type oftopography. Such dielectric structures are particularly suitable for thefabrication of capacitors, and more particularly for the fabrication ofcapacitors that can be embedded within a laminated printed circuitboard. Such capacitors contain a pair of electrodes (conductive layersor metal layers) on opposite sides of and in intimate contact with thecapacitor dielectric material.

[0018] Typically, the dielectric material useful in the presentdielectric structures is any that is suitable for use as capacitordielectric material, i.e. has a high dielectric constant. By “high”dielectric constant it is meant a dielectric constant ≧7, andpreferably >7. When a mutlilayer dielectric structure is used, it ispreferred that the structure has a dielectric constant ≧7, andpreferably >7. A wide variety of dielectric materials may suitably beused, including, but not limited to, polymers, ceramics, metal oxidesand combinations thereof. Suitable polymers include, but are not limitedto, epoxies, polyimides, polyurethanes, polyarylenes includingpolyarylene ethers, polysulfones, polysulfides, fluorinated polyimides,and fluorinated polyarylenes. Suitable ceramics and metal oxidesinclude, but are not limited to, titanium dioxide (“TiO₂”), tantalumoxides such as Ta₂O₅, barium-titanates having the formulaBa_(a)Ti_(b)O_(c) wherein a and b are independently from 0.75 to 1.25and c is 2.5 to 5, strontium-titanates such as SrTiO₃,barium-strontium-titanates, lead-zirconium-titanates such asPbZr_(y)Ti_(1-y)O₃, the series of doped lead-zirconium-titanates havingthe formula (Pb_(x)M_(1-x))(Zr_(y)Ti_(1-y))O₃ where M is any of avariety of metals such as alkaline earth metals and transition metalssuch as niobium and lanthanum, where x denotes lead content and ydenotes zirconium content, lithium-niobium oxides such as LiNbO₃,lead-magnesium-titanates such as (Pb_(x)Mg_(1-x))TiO₃, andlead-magnesium-niobium oxides such as (Pb_(x)Mg_(1-x))NbO₃ andlead-strontium titanates (Pb_(x)Sr_(1-x))TiO₃. When the capacitordielectric material includes Ba_(a)Ti_(b)O_(c), it is preferred that aand b are both 1 and c is 3, i.e. BaTiO₃. It is preferred that thedielectric material includes a ceramic or metal oxide. Such dielectricmaterials may be used in a variety of crystal structures including,without limitation, perovskites (ABO₃), pyrochlores (A₂B₂O₇), rutile andother structural polymorphs that have suitable electrical properties foruse as a capacitor dielectric.

[0019] When a polymer/ceramic or metal oxide composite capacitordielectric material is used, the ceramic or metal oxide material may beblended as a powder with the polymer. When the ceramic or metal oxide isused without a polymer, such ceramic or metal oxide may be deposited bya variety of means, such as, but not limited to, sol-gel, physicaland/or reactive evaporation, sputtering, laser-based depositiontechniques, chemical vapor deposition (“CVD”), combustion chemical vapordeposition (“CCVD”), controlled atmosphere combustion chemical vapordeposition (“CACCVD”), hydride vapor phase deposition, liquid phaseepitaxy, and electro-epitaxy. Preferably, such ceramic or metal oxidematerial is deposited as using sol-gel techniques.

[0020] In such sol-gel processes, as exemplified herein by thedeposition of a barium titanate capacitor dielectric, a non-aqueoussolution of titanium alkoxide is reacted with a barium precursor at thedesired stoichiometry and controllably hydrolyzed with a solvent/watersolution. A thin, adherent film of the hydrolyzed alkoxide solution (or“sol”) is then applied to the substrate by either dip-coating orspin-coating at 1,000 to 3,000 rpm. Multiple coatings may be requiredfor increased film thicknesses; the films are heated from 200 to 600° C.for 5 to 10 minutes to volatize the organic species and to render thedried “gel” film. While the majority of the organic matter and water isremoved from the films heating to 500° C.; the barium titanate film isstill only partially crystalline.

[0021] The film is preferably further annealed to improve the film'scrystallinity. This latter step involves heating the film such as at arate of 200° C./hr under dry nitrogen to a final annealing temperatureof 600 to 900° C., preferably 850° C., until the desired crystallizationis achieved. Alternatively, the film can be annealed via rapid thermalannealing (RTA).

[0022] Preferred as the titanium alkoxide is titanium isopropoxide. The“barium precursor” is typically the reaction product of a glycol andbarium oxide. Typical glycols are ethylene glycol and propylene glycol.The glycol-barium oxide reaction product is typically diluted with analcohol, glycol ethers and the like prior to the addition of thetitanium alkoxide. Suitable alcohols for use as diluents include,without limitation, ethanol, isopropyl alcohol, methanol, butanol andpentanol. Suitable glycol ethers include, but are not limited to,ethylene glycol butyl ether, propylene glycol t-butyl ether, propyleneglycol monomethyl ether, propylene glycol monomethyl ether acetate, andpropylene glycol butyl ether.

[0023] During the sol-gel process, the thickness of the composite is afunction of the rotation rate and the viscosity of the solution.Typically, the thickness of the composite is at least 100 nm, moretypically at least 250 nm, and still more typically at least 500 nm. Aparticularly useful thickness is in the range of 450 to 700 nm, and morepreferably from 475 to 600 nm. The maximum thickness, for instance of aplanar thin film composite, may be determined by the number of sol-gellayers deposited onto the substrate.

[0024] In an embodiment, a fine powder of barium oxide is added to theglycol. The reaction is exothermic and the reaction mixture iscontinuously stirred. The reaction mixture is then diluted with analkanol, such as 2-propanol. In addition, the titanium alkoxide is thenadded. To avoid rapid precipitation, the saturated glycol solution iskept at an elevated temperature, preferably 70° C. The solution is thenspin coated onto a suitable substrate. In the first stage of spincoating, the solution is added at approximately 2000 rpm for a shortduration. In the second stage, the rotation is increased to 4000 rpm fora time sufficient to achieve uniform deposition of film. The film isthen dried at a temperature of 80 to 100° C., preferably at 90° C. Theproduct is then subjected to a similar annealing stage as describedabove.

[0025] In another embodiment of the invention, the coating of thesubstrate is prepared by first dissolving a reaction mixture of alcohol,barium diacetate and titanium alkoxide in ambient atmosphere. Thesolution of alkanol, acetic acid glycerol is then continuously stirred.Barium acetate is then dissolved in the mixed solution. Titaniumalkoxide, such as titanium butoxide, is then added to the solution. Thesolution is continuously stirred for at least a couple of hours. Thesolution is then diluted with anhydrous alcohol, such as anhydrousmethanol, acetic acid and glycerol in the approximate weight ratio of5:5:1. The solution is then spin coated onto a suitable substrate,typically a bottom electrode or metal layer. The spinning is preferablydone at multiple stages. In the first stage, the solution is appliedonto the substrate at approximately 2000 rpm for 10 sec. In the secondstage, the solution is applied at a speed of 4000 rpm for a period oftime to achieve uniform deposition, generally about ten seconds. Thesols may also be applied to the substrate by roller coating or screenprinting, among other methods.

[0026] Alternatively, the substrate to be coated with the capacitordielectric may be dipped into the solution at an average speed of 2 to12 cm/min (1 to 5 in/min) and preferably from 2 to 8 cm/min. The coatingis then dried onto the substrate at a temperature of from 200 to 500°C.; typically films are first dried at 200° C. for 2 hours, and thenbaked at 400° C. for 20 minutes to remove volatile organic materials.Films are then annealed at the temperature range of 600 to 800° C. toimprove crystallinity. Typically, the duration of annealing is about onehour.

[0027] The dielectric structures of the present invention may contain asingle capacitor dielectric layer, or multiple dielectric layers. Whenmultiple capacitor dielectric layers are used, it is preferred that thetopmost capacitor dielectric layer, i.e. the dielectric layer to beplated with a conductive layer, has a textured surface. Such multilayerstructures preferably comprise a plurality of dielectric layers. In oneembodiment, it is further preferred that both the top and bottomdielectric layers in the multilayer dielectric structure have a texturedsurface.

[0028] Particularly suitable multilayer dielectric structures are thosehaving a first or top dielectric layer, a second or middle dielectriclayer and a third or bottom dielectric layer, wherein at least one ofthe top and bottom dielectric layers has textured surfaces. It will beappreciated by those skilled in the art that such middle dielectriclayer may comprise a single dielectric layer or a plurality ofdielectric layers. Such plurality of dielectric layers allows for thefabrication of a dielectric structure having a tailored overalldielectric constant.

[0029] When multiple dielectric layers are used, each of the dielectriclayers may be the same or different. In one embodiment, it is preferredthat the dielectric layers comprise the same dielectric materials. In analternate embodiment, it is preferred that different dielectricmaterials are used to form the various dielectric layers. An example ofa suitable combination of different dielectric materials are alternatinglayers of one or more of alumina, zirconia, barium-strontium-titanate,lead-zirconium-titanate, and lead-lanthanum-zirconium-titanate either bythemselves or in combination with one or more other dielectric layers.

[0030] In one embodiment, the present textured dielectric layer may beused as the topmost layer in the dielectric stack to improve theadhesion of a subsequently applied layer, such as a metal layer. In thisembodiment, the layers under the textured dielectric material may bedeposited by any suitable means, such as, but not limited to, sol-geltechniques, chemical vapor deposition, combustion chemical vapordeposition or any combination of these. Such dielectric layers under thetextured dielectric layer may be composed of any suitable dielectricmaterial which may be the same as, or different from, the dielectricmaterial used in the textured dielectric layer.

[0031] The overall thickness of the dielectric structure depends uponthe capacitor dielectric material selected as well as the totalcapacitance desired. In multilayer dielectric structures, the dielectriclayers may be of uniform thickness or varying thickness. Such structuresmay consist of many thin layers, one or more thick layers or a mixtureof thick and thin layers. Such selections are well within the ability ofthose skilled in the art. Exemplary dielectric layers may have athickness of 0.01 to 100 μm.

[0032] Such textured surface of the capacitor dielectric materialprovides increased adhesion for subsequently deposited or platedelectrode layers. Typically, the texturing of the dielectric layersurface is sufficient to increase the total surface area of thedielectric layer by at least 5% as compared to the same dielectric layerwithout such texturing. Preferably, the texturing is sufficient toincrease the total surface area by at least 10%, more preferably by atleast 15%, still more preferably by at least 20%, and further preferablyby at least 25%. The greater the increase in surface area of thedielectric layer, the greater the adhesion of the plated electrode ormetallization layer.

[0033] Capacitor dielectric surfaces may be textured by a variety ofmeans, including, but not limited to, laser structuring, use ofremovable porogens, and mechanical means such as physical abrasion.Methods that provide a suitably textured surface while providing controlof the resulting dielectric constant are preferred. Thus, laserstructuring and use of removable porogens are preferred means oftexturing the capacitor dielectric surfaces with the use of removableporogens being more preferred.

[0034] Laser structuring of the dielectric surface may be by any laserstructuring or ablation methods known in the art. In such methods, thelast capacitor dielectric layer applied to the dielectric structure issubjected to laser structuring, such as laser ablation, prior to thedeposition of an electrode (metallization) layer. Such laser ablation istypically computer controlled, thus allowing removal of precise amountsof capacitor dielectric material in a predetermined pattern. Suchpatterns include, without limitations, grooves, dimples, ripples, andcross-hatching.

[0035] Preferably, the textured surface is provided by removableporogens. In such method, the porogens, which are incorporated into thecapacitor dielectric material, are removed from the capacitor dielectricmaterial prior to deposition of the electrode or conductive layer. Uponremoval of the porogens, a capacitor dielectric material having pores,voids, free-volume or other forms of texturing is obtained. Suchporogens are particularly suitable for use with sol-gel techniques ofcapacitor dielectric material deposition, as described above.

[0036] A wide variety of removable porogens may be used in the presentinvention. Any material which can be dispersed within, suspended within,co-dissolved with, or otherwise combined with the capacitor dielectricand subsequently removed from the capacitor dielectric material maysuitably be used. Particularly suitable as removable porogens areorganic polymers or compounds which can be selectively etched or removedin the presence of the dielectric layer matrix and preferably withoutadversely affecting the dielectric matrix layer. Preferably, theremovable porogen is selected such that it is substantiallynon-aggregated or nonagglomerated in the capacitor dielectric material.Such non-aggregation or non-agglomeration reduces or avoids the problemof channel formation in the dielectric matrix. It is preferred that theremovable porogen is a polymer particle. It is further preferred thatthe porogen polymer particle is soluble or miscible in the solvent usedto deposit the sol.

[0037] The removable porogens may be polymers such as linear polymers,star polymers, dendritic polymers and polymeric particles, or may bemonomers or polymers that are copolymerized with a dielectric monomer toform a block copolymer having a labile (removable) component or may behigh boiling solvents. In an alternative embodiment, the porogen may bepre-polymerized or pre-reacted with the dielectric precursor to form thesol which may be monomeric, oligomeric or polymeric. Suchpre-polymerized material is then annealed to form a dielectric layer.

[0038] Suitable block copolymers having labile components useful asremovable porogens are those disclosed in U.S. Pat. Nos. 5,776,990 and6,093,636. Such block copolymers may be prepared, for example, by usingas pore forming material highly branched aliphatic esters that havefunctional groups that are further functionalized with appropriatereactive groups such that the functionalized aliphatic esters areincorporated into, i.e. copolymerized with, the vitrifying matrix. Suchblock copolymers include, but are not limited to, benzocyclobutenes,poly(aryl esters), poly(ether ketones), polycarbonates, polynorbornenes,poly(arylene ethers), polyaromatic hydrocarbons, such aspolynaphthalene, polyquinoxalines, poly(perfluorinated hydrocarbons)such as poly(tetrafluoroethylene), polyimides, polybenzoxazoles andpolycycloolefins.

[0039] Particularly suitable porogens are cross-linked polymerparticles, such as those disclosed in U.S. Pat. No. 6,271,273 B1 (You etal.) and U.S. Pat. No. 6,420,441 (Allen et al.). The polymeric porogenscomprise as polymerized units one or more monomers and one or morecross-linking agents. Suitable monomers useful in preparing the porogensinclude, but are not limited to, (meth)acrylic acid, (meth)acrylamides,alkyl (meth)acrylates, alkenyl (meth)acrylates, aromatic(meth)acrylates, vinyl aromatic monomers, nitrogen-containing compoundsand their thio-analogs, substituted ethylene monomers, and aromaticmonomers. Such porogens may be prepared by a variety of polymerizationmethods, including emulsion polymerization and solution polymerization,and preferably by solution polymerization.

[0040] Such porogens typically have a molecular weight in the range of5,000 to 1,000,000, preferably 10,000 to 500,000, and more preferably10,000 to 100,000. When polymeric particles are used as the porogens,they may be used in any of a variety of mean particles sizes, such as upto 1000 nm. Typical mean particle size ranges are from about 0.5 toabout 1000 nm, preferably from about 0.5 to about 200 nm, morepreferably from about 0.5 to about 50 nm, and most preferably from about1 nm to about 20 nm.

[0041] The porogen particles are typically cross-linked. Typically, theamount of cross-linking agent is at least about 1% by weight, based onthe weight of the porogen. Up to and including 100% cross-linking agent,based on the weight of the porogen, may be effectively used in theparticles of the present invention. It is preferred that the amount ofcross-linker is from about 1% to about 80%, and more preferably fromabout 1% to about 60%. A wide variety of cross-linking may be used. Suchcross-linking agents are multi-functional monomers and are well-known tothose skilled in the art. Exemplary cross-linking agents are disclosedin U.S. Pat. No. 6,271,273 (You et al.).

[0042] Porogen particles having a wide range of particle sizes may beused in the present invention. The particle size polydispersity of thesematerials is in the range of 1 to 20, preferably 1.001 to 15, and morepreferably 1.001 to 10. It will be appreciated that particles having auniform particle size distribution (a particle size polydispersity of 1to 1.5) or a broad particle size distribution may be effectively used inthe present invention.

[0043] It will be appreciated by those skilled in the art that theremovable porogens may remain dispersed with the gel or may beincorporated into the sol or gel.

[0044] The removable porogens are typically added to the sols in anamount sufficient to provide the desired texturing of the capacitordielectric surface. For example, the porogens may be added to the solsin any amount of from about 1 to about 60 wt %, based on the weight ofthe sol, preferably from 5 to 50 wt %, more preferably from 10 to 45 wt%, and even more preferably from 10 to 40 wt %.

[0045] The porogens may be combined with the ceramic precursors at anystage up to and even during the deposition of the sols to form a film.Such porogens may be combined with the ceramic precursors in anysuitable solvent, such as methyl isobutyl ketone, diisobutyl ketone,2-heptanone, γ-butyrolactone, γ-caprolactone, ethyl lactatepropyleneglycol monomethyl ether acetate, propyleneglycol monomethylether, diphenyl ether, anisole, n-amyl acetate, n-butyl acetate,cyclohexanone, N-methyl-2-pyrrolidone, N,N′dimethylpropyleneurea,mesitylene, xylenes, or mixtures thereof.

[0046] To be useful as porogens in forming the textured capacitordielectric materials, the porogens of the present invention must be atleast partially removable under conditions which do not adversely affectthe dielectric material, preferably substantially removable, and morepreferably completely removable. By “removable” is meant that thepolymer depolymerizes or otherwise breaks down into volatile componentsor fragments which are then removed from, or migrate out of, thedielectric material yielding pores or voids. Such resulting pores orvoids may fill with any carrier gas used in the removal process. Anyprocedures or conditions which at least partially remove the porogenwithout substantially degrading the dielectric material, that is, whereless than 5% by weight of the dielectric material is lost, may be used.It is preferred that the porogen is substantially removed. Typicalmethods of removal include, but are not limited to: chemical etching,exposure to heat, pressure or radiation such as, but not limited to,actinic, IR, microwave, UV, x-ray, gamma ray, alpha particles, orelectron beam. It will be appreciated that more than one method ofremoving the porogen or polymer may be used, such as a combination ofheat and actinic radiation. It is preferred that the dielectric materialis exposed to heat to remove the porogen. It will also be appreciated bythose skilled in the art that other methods of porogen removal may beemployed.

[0047] The porogens of the present invention can be thermally removedunder a variety of atmospheres, including but not limited to, vacuum,air, nitrogen, argon, mixtures of nitrogen and hydrogen, such as forminggas, or other inert or reducing atmosphere, as well as under oxidizingatmospheres. Preferably, the porogens are removed under inert orreducing atmospheres. It is preferred that the porogens of the presentinvention are removed at a temperature at or near that temperature usedto form the “gels”. Typically, the porogens of the present invention maybe removed at a wide range of temperatures such as from 150° to 650° C.,and preferably from 300° to 500° C. Such heating may be provided bymeans of an oven, flame, microwave and the like. It will be recognizedby those skilled in the art that the particular removal temperature of athermally labile porogen will vary according to composition of theporogen. For example, increasing the aromatic character of the porogenand/or the extent of cross-linking will increase the removal temperatureof the porogen. Thus, the removal temperature of the porogen may betailored to the temperature used to form a particular gel. Typically,the porogens of the present invention are removed upon heating for aperiod of time in the range of 1 to 120 minutes. After removal from thedielectric matrix material, 0 to 20% by weight of the porogen typicallyremains in the porous dielectric material. Residual porogen remainingwill be further removed during the annealing (or crystallization) stepof the sol-gel process.

[0048] Upon removal of the porogens, a textured dielectric materialhaving voids or other texturing is obtained, where the size of the voidsis preferably substantially the same as the particle size of theporogen. In general, pore sizes of up to 1,000 nm, such as that having amean particle size in the range of 0.5 to 1000 nm, are obtained. It ispreferred that the mean pore size is in the range of 0.5 to 200 nm, morepreferably from 0.5 to 50 nm, and most preferably from 1 nm to 20 nm.

[0049] The resulting dielectric material having voids or other texturingthus has an increased surface area as compared to such material withoutsuch voids. Such voids will be dispersed throughout the capacitordielectric material, including having a fraction at the surface of thematerial. If only one layer of capacitor dielectric material is used,texturing should not be accomplished through the use of porogens aschannels will likely develop which could lead to shorts duringsubsequent metallization to form the electrodes. Porogens are thususeful to provide a texturized surface in the top capacitor dielectriclayer in a multilayer dielectric structure. Preferably, the thickness ofthe textured dielectric layer is <50% of the total thickness of thedielectric structure. It is further preferred that the thickness of thetextured dielectric layer is <40%, more preferably <30% and still morepreferably <25% of the total thickness of the dielectric structure. Thereduction in dielectric constant caused by the introduction of air voids(with a dielectric constant of 1) is limited by the small volume of thetotal dielectric material that is so modified.

[0050] In an alternate embodiment, the porogen may be a solvent such asan alcohol, provided that such alcohol is sufficiently non-volatile thatit at least partially remains in the gel. Neopentyl alcohol is oneexample, however, other alcohols having similar properties may be used.

[0051]FIG. 1 illustrates a multilayer dielectric structure having aplurality of non-textured dielectric layers 5 where the top or firstdielectric layer 10 contains surface texturing (pores) 15. Suchdielectric structure is prepared by applying a series of sols to asubstrate which were then heated to form gel layers. A final solcontaining removable polymeric porogen is then applied and the polymericporogen particles are then thermally removed during the heating step toform the gel. The entire dielectric structure may then be heated toprovide the dielectric structure having the desired crystal structure.In an alternate embodiment, the non-porogen containing gel layers arefirst annealed to form the desired crytallinity, followed by depositionof the porogen-containing sol. The porogen-containing sol is then heated(first annealing) to form the gel and to remove the porogen and form atextured (porous) top dielectric layer. The porous top dielectric layeris then annealed to provide the desired crystallinity.

[0052] Electrodes (or conductive layers) may be deposited on the presentdielectric structures having a textured surface by a variety of methods,such as, but not limited to, electroless plating, electrolytic plating,chemical vapor deposition, physical vapor deposition and sol-geldeposition. When conductive polymers are used to form the conductivelayer, they may be deposited as a melt, in a solvent, by roller coating,as a dry film or by any other polymer coating technique. Electrolessplating may suitably be accomplished by a variety of known methods.Suitable metals that can be electrolessly plated include, but are notlimited to, copper, gold, silver, nickel, palladium, tin, and lead.Alternatively, a suitable conductive catalyst my be applied to thetextured dielectric surface to provide for electrolytic deposition of asuitable conductive electrode material. Preferably, the electrode isdeposited by electroless deposition. Such electroless deposition may befollowed by electrolytic deposition to build up a thicker metal deposit.The electrolytically deposited metal may be the same as or differentfrom the electrolessly deposited metal.

[0053] Also contemplated by the present invention is a capacitorcomprising a dielectric structure having a bottom surface and a texturedtop surface, a bottom conductive layer in intimate contact with thedielectric bottom surface and a top conductive layer in intimate contactwith the textured top dielectric surface. FIG. 2 illustrates a furtheralternate embodiment of a capacitor comprising a multilayer dielectricstructure having bottom dielectric layers 20 and a top dielectric 25having a textured surface 30, a bottom conductive layer 35 in intimatecontact with the surface of the bottom dielectric layers and a topconductive layer 40 in intimate contact with the textured top dielectricstructure surface.

[0054] An advantage of the present invention is that the increasedsurface area of the capacitor dielectric material provides for increasedadhesion of the metal layer to the capacitor dielectric. Thus, thepresent invention provides a method of improving the adhesion of aplated electrode to a dielectric layer comprising the steps ofdepositing on a substrate a dielectric layer comprising porogen,removing the porogen to provide a dielectric layer having a texturedsurface, and plating an electrode on the surface of the dielectriclayer.

[0055] A further advantage of the present invention is that thetexturing of the dielectric layer can be controlled to the depth of asingle layer in a multilayer dielectric stack. In general, when thetextured dielectric layer is the topmost layer of a dielectric stack,the surface of the textured layer is in contact with the dielectricstack is generally planar, but such surface may show texturing.

[0056] In another embodiment, the removable porogen is selected suchthat it preferentially migrates toward the top surface of the dielectriclayer during gel formation. In this way, the concentration of removablepolymer at or near the surface of the gel is increased as compared tothe concentration of the removal porogen in the bulk of the gel. Thisresults in an increase in pores or voids at or near the surface of thedielectric layer upon removal of the porogen. This embodiment providesthe texturing at or near the surface of the dielectric layer where it ismost needed for improved adhesion of a subsequently deposited metallayer.

[0057] In an alternate embodiment, the top dielectric layer mayoptionally contain a plating dopant. Such plating dopant is anyconductive element or compound present in the dielectric layer in anamount sufficient to promote metal plating of the surface of thedielectric layer. Suitable plating dopants include, but are not limitedto, metals such as tin, lead, palladium, cobalt, copper, silver, goldand alloys thereof, metal oxides such as zinc oxide, and mixturesthereof.

[0058] In another embodiment, the plating dopant may be incorporatedinto the porogen. By “incorporated” it is meant that the plating dopantis combined with the porogen, copolymerized with the monomers used tofrom the porogen reacted with the porogen, adsorbed onto the porogen,and encapsulated within the porogen, as well as other possiblecombinations. In one example, a plating dopant may be encapsulatedwithin the polymeric shell, such as is disclosed in U.S. Pat. No.5,835,174 (Clikeman et al.). An advantage of incorporating the platingdopant into the porogen is that the plating dopant may be more easilydispersed in the dielectric material and the plating dopant will remainin the pores or voids remaining after removal of the porogen.

[0059] The capacitors of the present invention are particularly suitablefor use as embedded capacitors in laminated printed circuit boards. Suchcapacitors are embedded in a laminate dielectric during the manufactureof laminated printed circuit boards. The laminate dielectrics aretypically organic polymers such as, but not limited to, epoxies,polyimides, fiber reinforced epoxies and other organic polymers used asdielectrics in printed circuit board manufacture. In general, laminatedielectrics have a dielectric constant ≦6, and typically have adielectric constant in the range of 3 to 6. The present capacitors maybe embedded by a variety of means known in the art, such as thosedisclosed in U.S. Pat. No. 5,155,655 (Howard et al.).

[0060] Accordingly, the present invention provides a method ofmanufacturing a multilayer printed wiring circuit board including thestep of embedding a capacitance material in one or more layers of themultilayer printed circuit board, wherein the capacitance materialincludes a multilayer dielectric structure including a first dielectriclayer and a second dielectric layer wherein the first dielectric layerhas a textured surface.

[0061] The following examples are presented to illustrate furthervarious aspects of the present invention, but are not intended to limitthe scope of the invention in any aspect.

EXAMPLE 1

[0062] Barium acetate, Ba(CH₃COO)₂, (1 mol) is dissolved in a mixedsolution of 20 mol ethanol, 25 mol acetic acid, and 1 mol glycerol, andthen the solution is stirred for 2 hr. After stirring, 1 mol ofTi[O(CH₂)₃CH₃]₄ is added to the solution, followed by stirring foranother 2 hr to prepare a barium titanate sol.

[0063] A sample of this sol is spin coated on a conductive substrate at2000 rpm for 45 sec. After the solution is spin coated, the sample isheated at 170° C. for 1 hr in a nitrogen-gas atmosphere, followed by twosteps of successive annealing of 400° C. for 1 hr and 700° C. for 1 hrin air. The thickness of the annealed dielectric sample prepared usingthis procedure is ˜100 nm.

[0064] To another sample of the sol is added cross-linked polymericporogen particles. The porogen particles are added in an amountsufficient to provide 40% porogen by weight, based on the total weightof the sol. The porogen particles contain as polymerized units one ormore alkyl (meth)acrylate monomers, one or more additional monomers anddivinylbenzene as the cross-linking agent. The porogen-containing sol isthen applied to the dielectric surface of the annealed dielectric sampleusing the conditions disclosed above. The sample is then processed at400° C. for 1 hr to both form the gel and remove the porogen. Finalphase transformation to the perovskite crystal structure is carried outat ≧700° C. to provide a dielectric structure having a textured surface.

EXAMPLE 2

[0065] The textured surface of the dielectric structure of Example 1 iscatalyzed and subjected to an electroless nickel plating bath to deposita layer of nickel on the textured surface. The nickel plated dielectricis next subjected to a nickel electroplating bath to increase thethickness of the nickel deposit.

EXAMPLE 3

[0066] The procedure of Example 2 is repeated except that theelectrolessly nickel plated dielectric is subjected to a copperelectroplating bath to deposit a layer of copper on the electrolessnickel layer.

EXAMPLE 4

[0067] The procedure of Example 3 is repeated except that theelectrolessly nickel plated dielectric is subjected to a silverelectroplating bath to deposit a layer of silver on the electrolessnickel layer.

EXAMPLE 5

[0068] The procedure of Example 2 is repeated except that theelectrolessly nickel plated dielectric is subjected to an immersion goldplating bath to deposit a layer of gold on the electroless nickel layer.

EXAMPLE 6

[0069] Lead acetate hydrate, Pb(CH₃COO)₂H₂O, is dissolved in2-methoxyethanol and is dehydrated at 110° C. under vacuum to providelead acetate. A solution of zirconium n-propoxide, Zr(n-OC₃H₇)₄, andtitanium isopropoxide, Ti(i-OC₃H₇)₄ in 2-methoxyethanol is prepared. Thezirconium-titanium solution is then added to the lead acetate solutionand the mixture is refluxed for 2 to 3 hours at 100° C. and is thendistilled to provide a PZT polymer precursor of the formulaPb(Zr_(0.52)Ti₀ ₄₈)O₃.

[0070] A 0.3M stock solution is prepared by dissolving the polymer intoluene. A sample of this sol is spin coated on a conductive substrate(aluminum) at 2000 rpm for 45 sec. After the solution is spin coated,the sample is dried at 200° C. for 5 to 10 minutes on a hot plate,followed by two steps of successive heating at of 450° C. for 20 minutesand 600° C. for 30 minutes in air. The thickness of the annealeddielectric sample prepared using this procedure is 100 nm. Cross-linkedpolymeric porogen particles are then added to another sample of the solin an amount sufficient to provide 35% porogen by weight, based on thetotal weight of the sol. The sol is then applied to the surface of thedielectric material on the aluminum substrate using the conditionsdisclosed above. The sample is then heated at 450° C. for 20 minutes to1 hour to both form the gel and remove the porogen. Final phasetransformation to the perovskite crystal structure is performed at 600°C. to provide a dielectric structure having a textured surface.

EXAMPLE 7

[0071] The procedure of Example 6 is repeated except that lanthanumisopropoxide (La(i-OC₃H₇)₃) is also added to the zirconium-titaniumsolution prior to the combination with the lead acetate solution. Alanthanum doped PZT polymer is obtained.

EXAMPLE 8

[0072] The procedure of Example 7 is repeated except that niobiumethoxide (Nb(OC₂H₅)₅) is used instead of lanthanum isopropoxide toprovide a niobium doped PZT polymer.

EXAMPLE 9

[0073] The procedure of Example 7 is repeated except that the conductivesubstrate is copper.

EXAMPLE 10

[0074] The procedure of Example 6 is repeated except that the conductivesubstrate is silver.

EXAMPLE 11

[0075] A solution of lanthanum nitrate hydrate (La(NO₃)₃.6H₂O) in2-methoxyethanol is prepared. A second solution of nickel acetatehydrate (Ni(OOCCH₃)₃.4H₂O) in 2-methoxyethanol is prepared. Eachcompound is then dehydrated and then the solutions are mixed in anamount to provide a stoichiometric ratio of La:Ni of 1:1. This lanthanumnickel sol is then spin coated on the texture surface of the dielectricstructure of Example 1 and annealed at 600° C. for 1 hour to provide alanthanum nickel oxide (LaNiO₃) conductive layer. This conductive layeris useful as an electrode.

EXAMPLE 12

[0076] The sample of Example 6 is subjected to an electroless copperbath to provide a layer of copper on the textured surface.

EXAMPLE 13

[0077] The sample of Example 1 is catalyzed and subjected to anelectroless nickel plating bath to deposit a layer of nickel on thetextured surface. The nickel plated sample is then contracted with animmersion gold plating bath to provide a gold layer over the nickellayer.

EXAMPLE 14

[0078] The procedure of Example 1 is repeated except that a star polymeris used as the porogen.

EXAMPLE 15

[0079] The procedure of Example 1 is repeated except thatpolyethyleneglycol is used as the porogen.

EXAMPLE 16

[0080] The sol of Example 1 is prepared but no porogen is added. The solis spin coated on a platinum foil and heated and annealed to theprocedure of Example 1. The surface of the dielectric layer is thensubjected to laser ablation to texturize the surface of the dielectriclayer. A copper conductive layer is then applied to the textured surfaceusing an electroless copper plating bath.

EXAMPLE 17

[0081] The procedure of Example 16 is repeated except that a layer ofconductive polymer is applied to the textured dielectric surface as anelectrode.

What is claimed is:
 1. A capacitor structure comprising a firstconductive layer, a second conductive layer and a multilayer dielectricstructure disposed between the first and second conductive layers,wherein the multilayer dielectric structure comprises a first dielectriclayer and a second dielectric layer, wherein the first dielectric layerhas a textured surface.
 2. The capacitor structure of claim 1 whereinthe first dielectric layer has a thickness of <50% of the totalthickness of the dielectric structure.
 3. The capacitor structure ofclaim 1 wherein the least one of the first and second dielectric layersis selected from the group consisting of polymers, ceramics, metaloxides and combinations thereof.
 4. The capacitor structure of claim 1wherein the dielectric structure has a dielectric constant of ≧7.
 5. Thecapacitor structure of claim 1 wherein the first conductive layer is inintimate contact with the textured surface of the first dielectriclayer.
 6. A method of improving the adhesion of a deposited conductivelayer to a dielectric structure comprising the steps of depositing on adielectric layer a top dielectric layer comprising porogen, removing theporogen to provide a textured surface on the top dielectric layer, andplating an electrode on the surface of the top dielectric layer.
 7. Themethod of claim 6 wherein the dielectric structure has a dielectricconstant of ≧7.
 8. The method of claim 6 wherein the top dielectriclayer is selected from the group consisting of polymers, ceramics, metaloxides and combinations thereof.
 9. The method of claim 6 wherein theporogen is a cross-linked polymer particle.
 10. The method of claim 9wherein the porogen has a mean particle size of up to 1000 nm.
 11. Themethod of claim 6 wherein the top dielectric layer has a thickness of<50% of the total thickness of the dielectric structure.
 12. The methodof claim 6 wherein the top dielectric layer further comprises a platingdopant.
 13. A printed circuit board comprising an embedded capacitancematerial, wherein the embedded capacitance material comprises amultilayer dielectric structure comprising a first dielectric layer anda second dielectric layer, wherein the first dielectric layer has atextured surface.
 14. The printed wiring board of claim 13 wherein aconductive layer is disposed on the textured surface of the firstdielectric layer.
 15. The printed wiring board of claim 13 wherein thefirst dielectric layer has a thickness of <50% of the total thickness ofthe dielectric structure.
 16. The printed wiring board of claim 13wherein the first dielectric layer is selected from the group consistingof polymers, ceramics, metal oxides and combinations thereof.
 17. Theprinted wiring board of claim 13 wherein the first dielectric layerfurther comprises a plating dopant.
 18. A method of manufacturing amultilayer printed circuit board comprising the step of embedding acapacitance material in one or more layers of the multilayer printedcircuit board, wherein the capacitance material comprises a multilayerdielectric structure comprising a first dielectric layer and a seconddielectric layer, wherein the first dielectric layer has a texturedsurface.
 19. The method of claim 18 further comprising the step ofdisposing a conductive layer on the textured surface of the firstdielectric layer.
 20. The method of claim 18 wherein the firstdielectric layer further comprises a plating dopant.